As a representative transition metal dichalcogenides(TMD),NiTe_(2)has an ultra-fast optical response,high carrier mobility,and excellent environmental stability.It has a broad application prospect in the fields of ene...As a representative transition metal dichalcogenides(TMD),NiTe_(2)has an ultra-fast optical response,high carrier mobility,and excellent environmental stability.It has a broad application prospect in the fields of ener-gy,biomedicine,optoelectronic devices,and so on.At present,there have been scant reports on the application of NiTe_(2)in the field of ultrafast photonics.In this work,NiTe_(2)was synthesized by chemical vapor deposition(CVD)and integrated with a tapered optical fiber to achieve mode-locking in an erbium-doped fiber laser(EDFL)and a thu-lium-doped fiber laser(TDFL).The mode-locked EDFL exhibited a pulse width of 678 fs and an output power of 3.92 mW.The pulse width of mode-locked TDFL was estimated to have a pulse width of 694 fs with an output power of 21.64 mW.These results demonstrate that NiTe_(2)is an effective saturable absorber material with potential applica-tions in the field of ultrafast optics.展开更多
In this paper,a conventional soliton(CS)mode-locked erbium-doped fiber(EDF)laser was de-veloped using MAX phase material(MAX-PM)Nb_(4)AlC_(3)as a saturable absorber(SA).First,the liquid phase exfoliation(LPE)method wa...In this paper,a conventional soliton(CS)mode-locked erbium-doped fiber(EDF)laser was de-veloped using MAX phase material(MAX-PM)Nb_(4)AlC_(3)as a saturable absorber(SA).First,the liquid phase exfoliation(LPE)method was utilized to prepare Nb_(4)AlC_(3)nanosheets,and then a piece of tapered fiber was adopted to fabricate Nb_(4)AlC_(3)-SA.It was found that the saturation intensity and modulation depth of the Nb_(4)AlC_(3)-SA are 2.02 MW/cm^(2)and 1.88%.Based on the Nb_(4)AlC_(3)-SA,a conventional soliton(CS)mode-locked EDF laser was achieved.The central wavelength,pulse duration,and pulse repetition rate were found to be 1565.65 nm,615.37 fs,and 24.63 MHz,respectively.The performance is competitive and particularly superior in terms of pulse duration.This study fully confirms that Nb_(4)AlC_(3)possesses marvellous nonlinear saturable absorption properties and opens new possibilities for further research on air-stable ultrafast photon-ic devices.展开更多
Multi-objective optimization(MOO)for the microwave metamaterial absorber(MMA)normally adopts evolutionary algo-rithms,and these optimization algorithms require many objec-tive function evaluations.To remedy this issue...Multi-objective optimization(MOO)for the microwave metamaterial absorber(MMA)normally adopts evolutionary algo-rithms,and these optimization algorithms require many objec-tive function evaluations.To remedy this issue,a surrogate-based MOO algorithm is proposed in this paper where Kriging models are employed to approximate objective functions.An efficient sampling strategy is presented to sequentially capture promising samples in the design region for exact evaluations.Firstly,new sample points are generated by the MOO on surro-gate models.Then,new samples are captured by exploiting each objective function.Furthermore,a weighted sum of the improvement of hypervolume(IHV)and the distance to sampled points is calculated to select the new sample.Compared with two well-known MOO algorithms,the proposed algorithm is vali-dated by benchmark problems.In addition,two broadband MMAs are applied to verify the feasibility and efficiency of the proposed algorithm.展开更多
The article deals with the motion of the breech block carrier and the weapon casing of an automatic weapon mounted on a flexible carriage and the base of the weapon.Earlier works,which did not consider the dynamic pro...The article deals with the motion of the breech block carrier and the weapon casing of an automatic weapon mounted on a flexible carriage and the base of the weapon.Earlier works,which did not consider the dynamic properties of the base of the weapon,did not allow to reconcile the calculated and experimental results of the weapon casing displacement when shooting from firing rests.For the analysis of the motion of individual parts,the methods of mathematical modelling and firing experiments using a high-speed camera were chosen.Calculations show the best accord with experiment when modelling the system with 4 degrees of freedom.The oscillation of the system regarding the movement of the breech block carrier and the weapon casing was investigated under changed conditions of rate of fire,the use of a muzzle brake and different types of shock absorbers.The velocities and displacements of the weapon casing and the breech block carrier at different values of the impulse of the gases to the breech block carrier were determined.展开更多
SiC aerogel presents several advantageous features like lightweight and high temperature resistance when applied as microwave absorbing material.In this paper,SiC aerogel was prepared eventually followed by the sol-ge...SiC aerogel presents several advantageous features like lightweight and high temperature resistance when applied as microwave absorbing material.In this paper,SiC aerogel was prepared eventually followed by the sol-gel and carbonization reduction process.The results showed that the effective electromagnetic microwave absorption capacity of SiC aerogel was highly increased after being pyrolyzed at 1500℃,which presented a minimum reflection loss value of-57.80 dB at 3.10 mm and 9.86 GHz.Besides,the electromagnetic parameters of SiC aerogel with different paraffin ratios were discussed as well as the varying electromagnetic microwave absorption performances.The minimum reflection loss value first rose then fell as the SiC/paraffin ratio increased,which demonstrated the importance of SiC content.This study establishes the theoretical foundation for the subsequent functional application of SiC aerogel.展开更多
An ultrawideband reflectionless metamaterial absorber(MA)is proposed by replacing the metallic ground with the complementary split-ring resonator(CSRR)structure.The proposed MA exhibits-10 d B reflectivity spectrum fr...An ultrawideband reflectionless metamaterial absorber(MA)is proposed by replacing the metallic ground with the complementary split-ring resonator(CSRR)structure.The proposed MA exhibits-10 d B reflectivity spectrum from 1 GHz to 20 GHz,which maintains more than 90%absorption from 1.5 GHz to20 GHz.Furthermore,it achieves angle stability for TE and TM polarization at oblique incident angles up to 40°and 65°,respectively.To achieve broadband absorption spectrum,we have adopted a single-layer high-impedance surface(HIS)loaded with a double-layer magnetic material(MM)structure.To further realize the RCS reduction into a lower frequency range,we have employed the scattering cancellation technology into the traditional metallic ground.Finally,we have fabricated a sample exhibiting the 10 d B RCS reduction from 1 GHz to 20 GHz with a thickness of 10 mm.Measurement and simulation results confirm that the proposed MA exhibits excellent comprehensive performance,making it suitable for many practical applications.展开更多
In this work, the damage and penetration behavior of aluminum foam at various types of impact were examined through experiments. The impact energy of a striker was applied on the fixed aluminum foam having a thickness...In this work, the damage and penetration behavior of aluminum foam at various types of impact were examined through experiments. The impact energy of a striker was applied on the fixed aluminum foam having a thickness of 25 mm while increasing its impact by 2 J at each strike from 6 J to 16 J. The results show that the impact energies from 6 J to 12 J could not penetrate aluminum foam. However, the aluminum foam applied with the impact energy of 12 J incurred severe damages on its lower part. Finally, the aluminum foam applied with the impact energy of 14 J was penetrated. The striker having the impact energy of 6 J could penetrate aluminum foam around 10 mm. At this moment, aluminum foam could absorb the impact energy of around 9 J. When the impact energy of 14 J was applied on the aluminum foam, the aluminum foam was penetrated and it absorbed the impact energy of around 17.2 J. It is possible to create the safer structure against impact using the results of this work. The simulation results for the verification of the experimental results imply that the results for all the experiments in this work are reliable. It is possible to predict the structural safety of the aluminum foam for an impact if the impact behavior of aluminum foam performed in this work is utilized.展开更多
The present study deals with the experimental,finite element(FE)and analytical assessment of low ballistic impact response of proposed flexible‘green’composite make use of naturally available jute and rubber as the ...The present study deals with the experimental,finite element(FE)and analytical assessment of low ballistic impact response of proposed flexible‘green’composite make use of naturally available jute and rubber as the constituents of the composite with stacking sequences namely jute/rubber/jute(JRJ),jute/rubber/rubber/jute(JRRJ)and jute/rubber/jute/rubber/jute(JRJRJ).Ballistic impact tests were carried out by firing a conical projectile using a gas gun apparatus at lower range of ballistic impact regime.The ballistic impact response of the proposed flexible composites are assesses based on energy absorption and damage mechanism.Results revealed that inclusion of natural rubber aids in better energy absorption and mitigating the failure of the proposed composite.Among the three different stacking sequences of flexible composites considered,JRJRJ provides better ballistic performance compared to its counterparts.The damage study reveals that the main mechanism of failure involved in flexible composites is matrix tearing as opposed to matrix cracking in stiff composites indicating that the proposed flexible composites are free from catastrophic failure.Results obtained from experimental,FE and analytical approach pertaining to energy absorption and damage mechanism agree well with each other.The proposed flexible composites due to their exhibited energy absorption capabilities and damage mechanism are best suited as claddings for structural application subjected to impact with an aim of protecting the main structural component from being failed catastrophically.展开更多
Based on a first-order state-vector differential equation representation of Maxwell's equations, an analytical formulation is derived for the equivalent currents on an anisotropic material backed by a metal surfa...Based on a first-order state-vector differential equation representation of Maxwell's equations, an analytical formulation is derived for the equivalent currents on an anisotropic material backed by a metal surface, and the relation between two currents is also considered. These expressions are degenerated into the common forms for some simple cases. This effort will provide the theoretical preparation for the approximate calculation of electromagnetic scattering from a conducting object coated by an anisotropic material.展开更多
Based on the working principle and the damping characteristic of hydraulic shock absorber, a fluid structure interaction method was presented, which was used to analyze the microcosmic and high-frequency processing me...Based on the working principle and the damping characteristic of hydraulic shock absorber, a fluid structure interaction method was presented, which was used to analyze the microcosmic and high-frequency processing mechanism of fluid structure interaction between circulation valve and liquid of hydraulic shock absorber. The fluid mesh distortion was controlled by the CEL language, and the fluid struc^tre interaction mathematical model was established. The finite element model was established by ANSYS CFX software and was analyzed by dynamic mesh technique. The local sensitive computational area was meshed by prismatic grid, which could reduce the negative volume problem during the simulation. The circulation valve and liquid of hydraulic shock absorber were simulated and analyzed under the condition of sinusoidal inlet velocity loads. Flow characteristic and dynamics characteristic were obtained. The pressure distribution and the displacement of circulation value were obtained, and the acceleration curve of circulation valve was simulated and analyzed. The conformity of the final simulation results with the experimental datum indicates that this method is accurate and reliable to analyze the dynamics characteristic between circulation valve and liquid of hydraulic shock absorber, which can provide a theoretical foundation for optimizing hydraulic shock absorber in the future.展开更多
Achieving high hitting accuracy for a main battle tank is challenging while the tank is on the move. This can be reached by proper design of a weapon control and gun system. In order to design an effective gun system ...Achieving high hitting accuracy for a main battle tank is challenging while the tank is on the move. This can be reached by proper design of a weapon control and gun system. In order to design an effective gun system while the tank is moving, better understanding of the dynamic behavior of the gun system is required. In this study, the dynamic behaviour of a gun system is discussed in this respect. Both experimental and numerical applications for the determination of the dynamic behaviour of a tank gun system are investigated. Methods such as the use of muzzle reference system(MRS) and vibration absorbers, and active vibration control technology for the control and the reduction of the muzzle tip deflections are also reviewed. For the existing gun systems without making substantial modifications,MRS could be useful in controlling the deflections of gun barrels with estimation/prediction algorithms.The vibration levels could be cut into half by the use of optimised vibration absorbers for an existing gun.A new gun system with a longer barrel can be as accurate as the one with a short barrel with the appropriate structural modifications.展开更多
This paper investigates the feasibility of using an active dynamic vibration absorber(ADVA) for active vibration control of a flexible missile system through simulation.Based on the principles of a dynamic vibration a...This paper investigates the feasibility of using an active dynamic vibration absorber(ADVA) for active vibration control of a flexible missile system through simulation.Based on the principles of a dynamic vibration absorber(DVA),a ring-type ADVA is first designed to attenuate the elastic vibration of the flexible missile,and the design of the active controller adopts the proportional-integral-derivative(PID)control algorithm.The motion equations of a flexible missile with an ADVA,which is subjected to follower thrust at its aft end,are derived using the Lagrangian approach.Taking the minimum of the root mean square(RMS) of the lateral displacement response of the center of mass as the objective function,a genetic algorithm(GA) is used to optimize the parameter of the DVA and PID controller.The numerical calculations show that the ADVA and DVA are effective in suppressing the vibration and provide approximately 41.2% and 17.6% improvement,respectively,compa red with the case of no DVA,The ADVA has better performance than the DVA,When the missile is subjected to follower thrust,the effect of vibration reduction is more effective than the case without follower thrust.It is feasible to reduce vibration and improve the stability of flexible missiles by means of the ADVA.展开更多
High frequency shock load is often generated during pyrotechnic device working, which is detrimental to spacecraft structures and electric devices. Therefore, it is valuable to reduce the shock load in pyrotechnic dev...High frequency shock load is often generated during pyrotechnic device working, which is detrimental to spacecraft structures and electric devices. Therefore, it is valuable to reduce the shock load in pyrotechnic device design. Actually, there are several ways to decrease pyroshock loads, such as reduction of powder,installation of buffering structure, insulation of damageable devices, and so on. Considered assuring the function of pyrotechnic device and minimum of structure modification, shock absorbing structure is more propitious to be introduced in pyrotechnic device. In this paper, based on the method of thinwalled metal tube diameter-expanding, a thin-walled tube shock buffering structure was designed on a separate bolt. Built on the simplified structure of a separate bolt, the model of cone piston impacting thin-walled tube absorber was established, and the thin-walled tube shock absorbing characteristics and the relation between cone angles and absorber performance were analyzed. The results showed that the change of buffering force of thin-walled tube could be divided into four phases, and each phase was correspondent to the cone piston structure. In addition, as the cone angle increases, the max shock acceleration changes in the style of decrease-increase-decrease-increase, which is the result of coupled effects of cone piston max enter depth, buffering force and energy loss. In short, these results could establish the relationships between thin-walled tube absorbing performance and its structure, which is of significance to develop low-shock pyrotechnic device.展开更多
Two kinds of nickel particles with flower-like struc~＇es assembled with a number of nano-flakes were synthesized and the relationship of their morphology and microwave absorbing properties was studied. The electromag...Two kinds of nickel particles with flower-like struc~＇es assembled with a number of nano-flakes were synthesized and the relationship of their morphology and microwave absorbing properties was studied. The electromagnetic parameters of these flower-like Ni were measured with vector network analyzer at 2-18 GHz frequency and the reflection losses （RL） with different sample thicknesses were calculated. The results indicate that the flower-like nickel-wax composites with the sample thickness less than 2 mm show excellent absorbing ability. This result is expected to play a guiding role in the preparation of the highly efficient absorber.展开更多
This paper gives an overview of the research at Institute of Acoustics, Tongji University, on functional absorbers and experience acquired in practical applications over the past three decades. Experiments and analysi...This paper gives an overview of the research at Institute of Acoustics, Tongji University, on functional absorbers and experience acquired in practical applications over the past three decades. Experiments and analysis of the absorption characteristics of three different geometrical forms of functional absorbers, i.e., panels, cubes and tubes, were conducted with different arrangements. The resulting esthetical effects are illustrated with pictures. Several non-fiber materials are used to compose functional absorbers with advantages both in acoustic properties and in architectural features. Cost effectiveness analysis is also given in order to provide design guidelines.展开更多
The article presents problems related to mechanical protection of vehicles with different add-on armours against chemical,biological and radiological contamination.This applies to vehicles with additional passive,reac...The article presents problems related to mechanical protection of vehicles with different add-on armours against chemical,biological and radiological contamination.This applies to vehicles with additional passive,reactive and hybrid protection in the form of cassettes against piercing with anti-tank projectiles,piercing with their kinetic energy of impact,and as a result of chemical energy of shaped charges as well as explosively formed projectiles.It has been shown how increased ballistic protection of these vehicles at the same time reduces their decontaminability in various places of the vehicle due to the increased additional surface of the vehicle with cassettes.Prevention of contamination of these cassettes has been presented as a way of reducing hard to reach surface for decontamination and a method of insulating construction elements(stands),fixing these cassettes to the vehicle,from the environment to prevent contact with contaminated liquids and dusts.The selection of appropriate materials is shown,which may affect the improvement of the decontamination efficiency of the vehicle with such cassettes.This applies to the use of materials with low absorption of chemical warfare agents,which prevent the accumulation of large amounts of these agents on contaminated surfaces and improve the effectiveness of decontamination.It also shows how to ensure better access of the disinfectant to as much of the vehicle surface as possible,covered with cassettes that have been contaminated.It shows how a vehicle,in particular with such cassettes,can provide protection against radar detection when Radar Absorbent Material is used on vehicle cassettes.展开更多
In order to discover the causes of the abnormal noise of shock absorbers, it is necessary to identify the operating characteristics of the shock absorbers. A micro-process model for operation of the hydraulic shock ab...In order to discover the causes of the abnormal noise of shock absorbers, it is necessary to identify the operating characteristics of the shock absorbers. A micro-process model for operation of the hydraulic shock absorber was presented. A novel concept, which describes the process of hydraulic shock absorber by dividing it into smaller steps, was proposed. The dynamic model and the differential equations were established. The results of numerical simulation agree well with data obtained from the vibrostand test, indicating that the collision between the piston and the oil, the alternation of static friction and sliding friction acted between the piston and the cylinder, and the adherence between valve plate and piston result in impact on the piston head near the top dead center and the bottom dead center. Ultimately, the impact excites the high-frequency vibration of the piston structure, which can generate the abnormal noise in the hydraulic shock absorber after its transfer. And the maximum vibration acceleration on the piston head and the abnormal noise increase with the increase of the gap between the oil and piston rod head, the maximum static friction force and the adhering function, respectively.展开更多
Numerical study was performed to evaluate the characteristics of combined heat transfer of radiation, conduction and convection in indirect near infrared ray （N/R） heating chamber. The effects of important design pa...Numerical study was performed to evaluate the characteristics of combined heat transfer of radiation, conduction and convection in indirect near infrared ray （N/R） heating chamber. The effects of important design parameters such as the shape of heat absorbing cylinder and heat releasing fin on the pressure drop and heat transfer coefficient were analyzed with different Reynolds numbers. The Reynolds numbers were varied from 103 to 3x106, which was defined based on the hydraulic diameter of the heat absorbing cylinder. Analyses were performed to obtain the inner and outer flow and the temperature distributions in the heat absorbing cylinder and the rates of radiation heat transfer and convection heat transfer. As the Reynolds number increases, the convection heat transfer rate is increased while the radiation heat transfer rate is decreased. The average convection heat transfer rate follows a power rule of the Reynolds number. Addition of three-dimensional heat releasing fin to the outside of the heat absorbing cylinder enhances the convection heat transfer.展开更多
基金Supported by Guangdong Basic and Applied Basic Research Fund,China(2024A1515012429)。
文摘As a representative transition metal dichalcogenides(TMD),NiTe_(2)has an ultra-fast optical response,high carrier mobility,and excellent environmental stability.It has a broad application prospect in the fields of ener-gy,biomedicine,optoelectronic devices,and so on.At present,there have been scant reports on the application of NiTe_(2)in the field of ultrafast photonics.In this work,NiTe_(2)was synthesized by chemical vapor deposition(CVD)and integrated with a tapered optical fiber to achieve mode-locking in an erbium-doped fiber laser(EDFL)and a thu-lium-doped fiber laser(TDFL).The mode-locked EDFL exhibited a pulse width of 678 fs and an output power of 3.92 mW.The pulse width of mode-locked TDFL was estimated to have a pulse width of 694 fs with an output power of 21.64 mW.These results demonstrate that NiTe_(2)is an effective saturable absorber material with potential applica-tions in the field of ultrafast optics.
文摘In this paper,a conventional soliton(CS)mode-locked erbium-doped fiber(EDF)laser was de-veloped using MAX phase material(MAX-PM)Nb_(4)AlC_(3)as a saturable absorber(SA).First,the liquid phase exfoliation(LPE)method was utilized to prepare Nb_(4)AlC_(3)nanosheets,and then a piece of tapered fiber was adopted to fabricate Nb_(4)AlC_(3)-SA.It was found that the saturation intensity and modulation depth of the Nb_(4)AlC_(3)-SA are 2.02 MW/cm^(2)and 1.88%.Based on the Nb_(4)AlC_(3)-SA,a conventional soliton(CS)mode-locked EDF laser was achieved.The central wavelength,pulse duration,and pulse repetition rate were found to be 1565.65 nm,615.37 fs,and 24.63 MHz,respectively.The performance is competitive and particularly superior in terms of pulse duration.This study fully confirms that Nb_(4)AlC_(3)possesses marvellous nonlinear saturable absorption properties and opens new possibilities for further research on air-stable ultrafast photon-ic devices.
基金supported by the National Key Research and Development Program(2021YFB3502500).
文摘Multi-objective optimization(MOO)for the microwave metamaterial absorber(MMA)normally adopts evolutionary algo-rithms,and these optimization algorithms require many objec-tive function evaluations.To remedy this issue,a surrogate-based MOO algorithm is proposed in this paper where Kriging models are employed to approximate objective functions.An efficient sampling strategy is presented to sequentially capture promising samples in the design region for exact evaluations.Firstly,new sample points are generated by the MOO on surro-gate models.Then,new samples are captured by exploiting each objective function.Furthermore,a weighted sum of the improvement of hypervolume(IHV)and the distance to sampled points is calculated to select the new sample.Compared with two well-known MOO algorithms,the proposed algorithm is vali-dated by benchmark problems.In addition,two broadband MMAs are applied to verify the feasibility and efficiency of the proposed algorithm.
基金supported by the Research project VAROPS(Military autonomous and robotic assets)of the Ministry of Defence of The Czech Republicby the Specific Research Support Project(Grant No.SV22-201)financed from funds of the Ministry of Education,Youth and Sports of The Czech Republic。
文摘The article deals with the motion of the breech block carrier and the weapon casing of an automatic weapon mounted on a flexible carriage and the base of the weapon.Earlier works,which did not consider the dynamic properties of the base of the weapon,did not allow to reconcile the calculated and experimental results of the weapon casing displacement when shooting from firing rests.For the analysis of the motion of individual parts,the methods of mathematical modelling and firing experiments using a high-speed camera were chosen.Calculations show the best accord with experiment when modelling the system with 4 degrees of freedom.The oscillation of the system regarding the movement of the breech block carrier and the weapon casing was investigated under changed conditions of rate of fire,the use of a muzzle brake and different types of shock absorbers.The velocities and displacements of the weapon casing and the breech block carrier at different values of the impulse of the gases to the breech block carrier were determined.
基金supported by various grants including the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2021A1515111155 and 2022A1515111200)Basic Research Programs of Taicang(Grant Nos.TC2023JC03 and TC2022JC08)+2 种基金Natural Science Foundation of Shaanxi Province(Grant No.2023JC-QN-0380)Nantong Natural Science Foundation(Grant No.JC2023011)Shanghai Central Guidance Fund for Local Science and Technology Development(Grant No.YDZX20233100004009)。
文摘SiC aerogel presents several advantageous features like lightweight and high temperature resistance when applied as microwave absorbing material.In this paper,SiC aerogel was prepared eventually followed by the sol-gel and carbonization reduction process.The results showed that the effective electromagnetic microwave absorption capacity of SiC aerogel was highly increased after being pyrolyzed at 1500℃,which presented a minimum reflection loss value of-57.80 dB at 3.10 mm and 9.86 GHz.Besides,the electromagnetic parameters of SiC aerogel with different paraffin ratios were discussed as well as the varying electromagnetic microwave absorption performances.The minimum reflection loss value first rose then fell as the SiC/paraffin ratio increased,which demonstrated the importance of SiC content.This study establishes the theoretical foundation for the subsequent functional application of SiC aerogel.
文摘An ultrawideband reflectionless metamaterial absorber(MA)is proposed by replacing the metallic ground with the complementary split-ring resonator(CSRR)structure.The proposed MA exhibits-10 d B reflectivity spectrum from 1 GHz to 20 GHz,which maintains more than 90%absorption from 1.5 GHz to20 GHz.Furthermore,it achieves angle stability for TE and TM polarization at oblique incident angles up to 40°and 65°,respectively.To achieve broadband absorption spectrum,we have adopted a single-layer high-impedance surface(HIS)loaded with a double-layer magnetic material(MM)structure.To further realize the RCS reduction into a lower frequency range,we have employed the scattering cancellation technology into the traditional metallic ground.Finally,we have fabricated a sample exhibiting the 10 d B RCS reduction from 1 GHz to 20 GHz with a thickness of 10 mm.Measurement and simulation results confirm that the proposed MA exhibits excellent comprehensive performance,making it suitable for many practical applications.
基金Project(2011-0006548)supported by the Basic Research Program through the National Research Foundation of Korea
文摘In this work, the damage and penetration behavior of aluminum foam at various types of impact were examined through experiments. The impact energy of a striker was applied on the fixed aluminum foam having a thickness of 25 mm while increasing its impact by 2 J at each strike from 6 J to 16 J. The results show that the impact energies from 6 J to 12 J could not penetrate aluminum foam. However, the aluminum foam applied with the impact energy of 12 J incurred severe damages on its lower part. Finally, the aluminum foam applied with the impact energy of 14 J was penetrated. The striker having the impact energy of 6 J could penetrate aluminum foam around 10 mm. At this moment, aluminum foam could absorb the impact energy of around 9 J. When the impact energy of 14 J was applied on the aluminum foam, the aluminum foam was penetrated and it absorbed the impact energy of around 17.2 J. It is possible to create the safer structure against impact using the results of this work. The simulation results for the verification of the experimental results imply that the results for all the experiments in this work are reliable. It is possible to predict the structural safety of the aluminum foam for an impact if the impact behavior of aluminum foam performed in this work is utilized.
文摘The present study deals with the experimental,finite element(FE)and analytical assessment of low ballistic impact response of proposed flexible‘green’composite make use of naturally available jute and rubber as the constituents of the composite with stacking sequences namely jute/rubber/jute(JRJ),jute/rubber/rubber/jute(JRRJ)and jute/rubber/jute/rubber/jute(JRJRJ).Ballistic impact tests were carried out by firing a conical projectile using a gas gun apparatus at lower range of ballistic impact regime.The ballistic impact response of the proposed flexible composites are assesses based on energy absorption and damage mechanism.Results revealed that inclusion of natural rubber aids in better energy absorption and mitigating the failure of the proposed composite.Among the three different stacking sequences of flexible composites considered,JRJRJ provides better ballistic performance compared to its counterparts.The damage study reveals that the main mechanism of failure involved in flexible composites is matrix tearing as opposed to matrix cracking in stiff composites indicating that the proposed flexible composites are free from catastrophic failure.Results obtained from experimental,FE and analytical approach pertaining to energy absorption and damage mechanism agree well with each other.The proposed flexible composites due to their exhibited energy absorption capabilities and damage mechanism are best suited as claddings for structural application subjected to impact with an aim of protecting the main structural component from being failed catastrophically.
文摘Based on a first-order state-vector differential equation representation of Maxwell's equations, an analytical formulation is derived for the equivalent currents on an anisotropic material backed by a metal surface, and the relation between two currents is also considered. These expressions are degenerated into the common forms for some simple cases. This effort will provide the theoretical preparation for the approximate calculation of electromagnetic scattering from a conducting object coated by an anisotropic material.
基金Project(51275542) supported by the National Natural Science Foundation of Chinaproject(CDJXS12110010) supported by the Fundamental Research Funds for the Central Universities of China
文摘Based on the working principle and the damping characteristic of hydraulic shock absorber, a fluid structure interaction method was presented, which was used to analyze the microcosmic and high-frequency processing mechanism of fluid structure interaction between circulation valve and liquid of hydraulic shock absorber. The fluid mesh distortion was controlled by the CEL language, and the fluid struc^tre interaction mathematical model was established. The finite element model was established by ANSYS CFX software and was analyzed by dynamic mesh technique. The local sensitive computational area was meshed by prismatic grid, which could reduce the negative volume problem during the simulation. The circulation valve and liquid of hydraulic shock absorber were simulated and analyzed under the condition of sinusoidal inlet velocity loads. Flow characteristic and dynamics characteristic were obtained. The pressure distribution and the displacement of circulation value were obtained, and the acceleration curve of circulation valve was simulated and analyzed. The conformity of the final simulation results with the experimental datum indicates that this method is accurate and reliable to analyze the dynamics characteristic between circulation valve and liquid of hydraulic shock absorber, which can provide a theoretical foundation for optimizing hydraulic shock absorber in the future.
文摘Achieving high hitting accuracy for a main battle tank is challenging while the tank is on the move. This can be reached by proper design of a weapon control and gun system. In order to design an effective gun system while the tank is moving, better understanding of the dynamic behavior of the gun system is required. In this study, the dynamic behaviour of a gun system is discussed in this respect. Both experimental and numerical applications for the determination of the dynamic behaviour of a tank gun system are investigated. Methods such as the use of muzzle reference system(MRS) and vibration absorbers, and active vibration control technology for the control and the reduction of the muzzle tip deflections are also reviewed. For the existing gun systems without making substantial modifications,MRS could be useful in controlling the deflections of gun barrels with estimation/prediction algorithms.The vibration levels could be cut into half by the use of optimised vibration absorbers for an existing gun.A new gun system with a longer barrel can be as accurate as the one with a short barrel with the appropriate structural modifications.
基金supported by the National Natural Science Foundation of China(10972033)。
文摘This paper investigates the feasibility of using an active dynamic vibration absorber(ADVA) for active vibration control of a flexible missile system through simulation.Based on the principles of a dynamic vibration absorber(DVA),a ring-type ADVA is first designed to attenuate the elastic vibration of the flexible missile,and the design of the active controller adopts the proportional-integral-derivative(PID)control algorithm.The motion equations of a flexible missile with an ADVA,which is subjected to follower thrust at its aft end,are derived using the Lagrangian approach.Taking the minimum of the root mean square(RMS) of the lateral displacement response of the center of mass as the objective function,a genetic algorithm(GA) is used to optimize the parameter of the DVA and PID controller.The numerical calculations show that the ADVA and DVA are effective in suppressing the vibration and provide approximately 41.2% and 17.6% improvement,respectively,compa red with the case of no DVA,The ADVA has better performance than the DVA,When the missile is subjected to follower thrust,the effect of vibration reduction is more effective than the case without follower thrust.It is feasible to reduce vibration and improve the stability of flexible missiles by means of the ADVA.
文摘High frequency shock load is often generated during pyrotechnic device working, which is detrimental to spacecraft structures and electric devices. Therefore, it is valuable to reduce the shock load in pyrotechnic device design. Actually, there are several ways to decrease pyroshock loads, such as reduction of powder,installation of buffering structure, insulation of damageable devices, and so on. Considered assuring the function of pyrotechnic device and minimum of structure modification, shock absorbing structure is more propitious to be introduced in pyrotechnic device. In this paper, based on the method of thinwalled metal tube diameter-expanding, a thin-walled tube shock buffering structure was designed on a separate bolt. Built on the simplified structure of a separate bolt, the model of cone piston impacting thin-walled tube absorber was established, and the thin-walled tube shock absorbing characteristics and the relation between cone angles and absorber performance were analyzed. The results showed that the change of buffering force of thin-walled tube could be divided into four phases, and each phase was correspondent to the cone piston structure. In addition, as the cone angle increases, the max shock acceleration changes in the style of decrease-increase-decrease-increase, which is the result of coupled effects of cone piston max enter depth, buffering force and energy loss. In short, these results could establish the relationships between thin-walled tube absorbing performance and its structure, which is of significance to develop low-shock pyrotechnic device.
基金Project(JC201006020838A)supported by the Basic Research Funds of Science and Technology Foundation of Shenzhen,China
文摘Two kinds of nickel particles with flower-like struc~＇es assembled with a number of nano-flakes were synthesized and the relationship of their morphology and microwave absorbing properties was studied. The electromagnetic parameters of these flower-like Ni were measured with vector network analyzer at 2-18 GHz frequency and the reflection losses （RL） with different sample thicknesses were calculated. The results indicate that the flower-like nickel-wax composites with the sample thickness less than 2 mm show excellent absorbing ability. This result is expected to play a guiding role in the preparation of the highly efficient absorber.
文摘This paper gives an overview of the research at Institute of Acoustics, Tongji University, on functional absorbers and experience acquired in practical applications over the past three decades. Experiments and analysis of the absorption characteristics of three different geometrical forms of functional absorbers, i.e., panels, cubes and tubes, were conducted with different arrangements. The resulting esthetical effects are illustrated with pictures. Several non-fiber materials are used to compose functional absorbers with advantages both in acoustic properties and in architectural features. Cost effectiveness analysis is also given in order to provide design guidelines.
文摘The article presents problems related to mechanical protection of vehicles with different add-on armours against chemical,biological and radiological contamination.This applies to vehicles with additional passive,reactive and hybrid protection in the form of cassettes against piercing with anti-tank projectiles,piercing with their kinetic energy of impact,and as a result of chemical energy of shaped charges as well as explosively formed projectiles.It has been shown how increased ballistic protection of these vehicles at the same time reduces their decontaminability in various places of the vehicle due to the increased additional surface of the vehicle with cassettes.Prevention of contamination of these cassettes has been presented as a way of reducing hard to reach surface for decontamination and a method of insulating construction elements(stands),fixing these cassettes to the vehicle,from the environment to prevent contact with contaminated liquids and dusts.The selection of appropriate materials is shown,which may affect the improvement of the decontamination efficiency of the vehicle with such cassettes.This applies to the use of materials with low absorption of chemical warfare agents,which prevent the accumulation of large amounts of these agents on contaminated surfaces and improve the effectiveness of decontamination.It also shows how to ensure better access of the disinfectant to as much of the vehicle surface as possible,covered with cassettes that have been contaminated.It shows how a vehicle,in particular with such cassettes,can provide protection against radar detection when Radar Absorbent Material is used on vehicle cassettes.
基金Project(200244) supported by the Visiting Scholar Foundation of the State Key Laboratory of Mechanical Transmission, Chongqing University
文摘In order to discover the causes of the abnormal noise of shock absorbers, it is necessary to identify the operating characteristics of the shock absorbers. A micro-process model for operation of the hydraulic shock absorber was presented. A novel concept, which describes the process of hydraulic shock absorber by dividing it into smaller steps, was proposed. The dynamic model and the differential equations were established. The results of numerical simulation agree well with data obtained from the vibrostand test, indicating that the collision between the piston and the oil, the alternation of static friction and sliding friction acted between the piston and the cylinder, and the adherence between valve plate and piston result in impact on the piston head near the top dead center and the bottom dead center. Ultimately, the impact excites the high-frequency vibration of the piston structure, which can generate the abnormal noise in the hydraulic shock absorber after its transfer. And the maximum vibration acceleration on the piston head and the abnormal noise increase with the increase of the gap between the oil and piston rod head, the maximum static friction force and the adhering function, respectively.
基金supported by the Second Stage of Brain Korea 21 Projects
文摘Numerical study was performed to evaluate the characteristics of combined heat transfer of radiation, conduction and convection in indirect near infrared ray （N/R） heating chamber. The effects of important design parameters such as the shape of heat absorbing cylinder and heat releasing fin on the pressure drop and heat transfer coefficient were analyzed with different Reynolds numbers. The Reynolds numbers were varied from 103 to 3x106, which was defined based on the hydraulic diameter of the heat absorbing cylinder. Analyses were performed to obtain the inner and outer flow and the temperature distributions in the heat absorbing cylinder and the rates of radiation heat transfer and convection heat transfer. As the Reynolds number increases, the convection heat transfer rate is increased while the radiation heat transfer rate is decreased. The average convection heat transfer rate follows a power rule of the Reynolds number. Addition of three-dimensional heat releasing fin to the outside of the heat absorbing cylinder enhances the convection heat transfer.
